Seismic well logging data display



z3 Sheets-Sheet 1 R. L. GEYER ETAL ATTORNEY Dec. 7, 1965 SEISMlC WELLLOGGING DATA DISPLAY Original Filed Feb.

Dec. 7, 1965 R. GEYl-:R ETAL 2 Sheets-She Original Filed Feb. l, 1960SHALE SHALE FIG. 3

ROBERT L. GEYER NEIL R. SPARKS INVENTORS ATTORNEY United States Patent O25,928 SEISMIC WELL LUGGING DATA DISPLAY Robert L. Geyer and Neil R.Sparks, both of Tulsa, Okla., assignors to Pau American PetroleumCorporation, Tulsa, Gkla., a corporation of Delaware Original No.3,093,810, dated .lune 11, 1963, Ser. No. 5,882, Feb. 1, 1960.Application for reissue June 8, 1965, Ser. No. 463,069

16 Claims. (Cl. 340-48) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

This invention relates to seismic velocity well logging and is directedparticularly to a method and apparatus for obtaining and recordingimproved seismic velocity well logs. More specifically, the invention isdirected to irnprovements in the display of the data obtained.

Seismic velocity well logging as presently practiced comprisestransmitting a high-frequency acoustic impulse into the well-bore fluidsand the surrounding formations and detecting the first-arriving impulseat a detector in the Well a short distance away, typically about fivefeet. At such a distance a wave train of substantial length, made up ofa number of different wave arrivals, can be readily detccted. Only thefirst-arriving impulse is ordinarily utilized, however, since it is thewave which travels through the formations and thus indicates theformation compressional seismic-wave velocity. Nevertheless, it has beenrecognized that the later wave arrivals give by their frequencies,arrival times, and amplitudes, valuable additional information about thewell formations. Such later wave arrivals have been recorded along withthe iirstarriving impulses by photographing their form on the face of acathode ray oscilloscope, but such a display has the disadvantage thatit is of undue length. Further, it is only by a careful study of each ofa large number of individual oscillograms that changes in the formationlithology can be understood.

ln view of the foregoing it is a primary object of our invention toprovide a novel and improved method and apparatus for recording anddisplaying the data obtained in seismic velocity well logging. Moreparticularly, it is an object of our invention to provide a method andapparatus for recording and displaying the seismic velocity log data ina form which is both compact and complete as to the form and arrivaltimes of various waves of interest. Other and further objects, uses, andadvantages of the invention will become apparent as the descriptionproceeds.

Briey stated, the foregoing and other objects are accomplished byrecording the wave form of the received wave impulses asvariable-density traces which extend across the log record stripperpendicular to the depth dimension. Preferably, the pulse repetitionrate and speed of record strip movement are such that adjacent tracesoverlap appreciably, so that the resultant record presents an over-allintermediate density for zero signal amplitude, but which density variesbetween greater and smaller values for plus and minus values of thesignal amplitude.

A preferred apparatus for practicing our invention comprises means forphotographing the face of an oscilloscope tube on which the horizontalsweep is synchronized with the transmission of acoustic impulses throughthe subsurface formations, and the beam intensity is varied in ae- Re.25,928 Reissued Dec. 7, 1965 ICC cordance with variations in thereceived signal. In order to prevent density variations in the finalrecord due to variations in the logging speed, means are provided tovary the photographic exposure in accordance with the logging speedvariations.

This will be better understood by reference to the accompanying drawingsforming a part of this application and illustrating a typical embodimentof our invention and the results produced thereby. In these drawings,

FIGURE 1 is a diagrammatic illustration of a recording system andsubsurface logging instrument embodying our invention;

FIGURE 2 shows various wave forms typically observed in the operation ofthe invention; and

FIGURE 3 is a representation of a portion of a typical log obtained byour invention correlated with the lithology responsible for the observedwave forms.

Referring now to these drawings in detail and particulariy to FIGURE lthereof, in a well bore 10 is shown a logging instrument 11 comprisingessentially a pulse transmitter l2 and a pulse receiver 13 separated byan acoustic insulator 14. The spacing between transmitter 12 andreceiver 13 is typically about tive feet. In operation, the pulsetransmitter 12 is periodically actuated by a power supply 15 to transmitinto the bore hole fluids and the surrounding formations ahigh-frequency acoustic impulse, the time of starting of the impulsebeing transmitted to the ground surface over a lead 16. The resultingimpulses after travel by various paths to the receiver 13 arc amplifiedby an amplifier 17 connected thereto and transmitted over a lead 18 tothe ground surface. Typically, the leads 16 and 18 are insulated andcomprise parts of a cable 19 by which the instrument 11 is raised orlowered in the well 10.

At the ground surface the cable 19 passes over a measuring wheel 21 to adrum 22 where the lead 16 is brought out to a slip ring 23, while thelead 18 is brought out to a slip ring 24. By a brush and lead 25 theslip ring 23 is connected to a pulse amplier 26 while a brush and lead27 connect the slip ring 24 to a receiver signal amplifier 28.

The recording apparatus comprises a cathode-ray oscillograph tub 31having horizontal sweep electrodes 32 and a beam-intensity controlelectrode 33. A sweep voltage generator 34 triggered over the conductor35 from the pulse amplifier 26 transmits a sweep voltage over the lead36 to the electrodes 32. Similarly, the beam-intensity control electrode33 is connected to the output of receiver signal amplier 28 by the lead37. Accordingly, the intensity of the beam of tube 31 is varied inaccordance with the amplitude variations of the signal received at thereceiver 13. By triggering sweep generator 34 at the instant ofgeneration of the impulse by transmitter 12 through the systemdescribed, a linear trace 38 varying in intensity along its length ispresented on the face of oscilloscope 31.

By means of a mechanical connection 41, the depthmeasuring wheel 2l overwhich passes the cable 19 drives a direct-current electric generator 42to produce on the output leads 43 of the generator a voltage varying inamplitude with the rate of rotation of wheel 21 and thus with the speedof movement of the instrument 11 in well 10. The rotation of measuringwheel 21 is further transmitted by a connection 44 to a roller orsprocket 4S which drives a film or photosensitive paper strip 46 from asupply roll 47 to a takeup roll 48. Between the face of oscilloscope 31and lilm 46 is a lens system made up oi the elements Sla and 51h whichfocuses on the film or photosensitive paper 46 an image 52 of theoscilloscope trace 33. The transmission of light from the trace 38 tothe image 52 through the lenses 51a and Slb is controlled by a variablediaphragm 53 actuated from a diaphragm-control iechanism S4 whichresponds to the voltage on leads 43 of the generator 42.

In operation, the pulses emitted by transmitter 12 are normally sent outat a constant repetition rate, while the speeds of movement ofinstrument 11 through the well It) and of the tilm 46 are also usuallyconstant but sometimes may vary. In the absence of the diaphragm 53 andcontrol 54, and assuming that there is such overlap in successive passesof the image 52 that the density at any point is the result of severalexposures, variations in speed would result in a varying density of thephotographic record ot the image S2, over and above the variationsintroduced by modulation of the cathode-ray beam by the controlelectrode 33 in accordance with signal wave form. By regulating theopening of diaphragm 53 in proportion to the film movement or loggingspeed, however, as it is measured by the tachometer generator 42, theintensity of the light transmitted from trace 38 to the image 52 isvaried just sufficiently to compensate for the eflect of the speedchange. For example, if the logging speed and speed of movement of thefilm 46 increase, the diaphragm 53 opens sufliciently so that theadditional light transmitted through the lens system just compensatesfor what wouid otherwise be a reduction in accumulated exposure at anypoint of the i'ilm 46. As a result, the density variations of the film46 are independent of the speed of movement of the instrument 11 and ofthe film 46 and vary only with the wave form of the received signals. Aswill be apparent, the oscilloscope 31, the film 46 and its associatedmechanism, and the lens and diaphragm control 54 should be surrounded bya light-excluding box or enclosure schematically indicated by the dashedline 55.

While the system just described is a direct-recording system, in thatthe signals are immediately translated into intensity variations andrecorded while the logging proceeds, the same final presentation can bemade indirectly by storing the signals in reproducible form andreproducing them at any subsequent time. For example, the triggerpulses. received signals, and logging speed andV depth indications canbe flrst recorded on separate tracks of a magnetic tape, and laterreproduced by magnetic playback hearts, with or without additionalltering or other modifications or corrections, to provide thevariabledensity display of this invention.

In FIGURE 2 are shown examples of certain typical wave forms which arereported by Vogel in Geophysics, vol. XVII, page 58S, to have beenobserved in the course of subsurface seismic velocity logging. Thus, thetrace 61 is said to be typical of the form of the waves received by borehole instrument such as 11 when the surrounding formation is largelyclay. The event beginning at the time marked P is the first arrivalthrough the clay and is a compressional wave. The arrival beginning atthe time marked W, of considerably higher frequency than that startingat P, is the wave transmitted primarily through the bore-hole liquid.While the liquid-borne wave W is here shown of substantially lessamplitude than the compressional wave P, it may often be of quite largeamplitude.

The variable-density trace 62 adjacent the deectiongalvanonieter trace61 corresponds to the trace 61 and wave forms recorded therebytranslated into variabledensity or variable-intensity form. From end toend these traces correspond to a time span of about 2 milliseconds. Thisspan was considered appropriate for the instrument and spacingdimensions used, but may ditler for other instruments. The time elapsedbefore the beginning oi the wave at P is thc travel time of an acousticimpulse from the transmitter 12 to the receiver 13 primarily through theclay formation when the spacing between the source and receiver is aboutfive feet.

Deflectiori-galvanometer trace 63 is the same type ofV recording astrace 61 except that it is made in a shale formation. As before, theevents marked P and W correspond to the initiation of the compressionaland the water-borne waves, while the event marked R corresponds to thestart of a wave which is not identified on trace 61 but which isbelieved to be a Rayleigh-type wave that travels principally along thewell wall and is sometimes called a tube wave. As before, thevariable-intensity trace 64 corresponds in form to thevariable-dctlection trace 63. The earlier occurrence ot the P wave intrace 63, as compared with 61, corresponds to the higher value ofseismic compressional-wave velocity in shale as corripared with clay.

The trace 65 is similar to 6l and 63 except that it is the type of wavetrain recorded when the instrument 11 is surrounded by limestone ratherthan clay or shale. The various arrivals indicated by P, W, and R arethe same as those for the wave 63. In the case of limestone and similarcrystalline hard rocks, however, there is frequently also observed ashear-wave arrival, here designated by S. The relatively earlier arrivaltime of the P wave for limestone, as compared with its arrival in shalein trace 63, corresponds to the generally higher velocity of seismiccompressional waves in limestone as compared with shale. Trace 66corresponds to trace 65 but is in variable-density form.

It will be understood that the showing of this figure and of FIGURE 3 ishighly diagrammatic, in that the numerous gradations of densitycorresponding to the dctails of the wave form of the trace 65 cannot besatisfactorily shown by the inked-line drawing, whereas they will beapparent in a photographic recording of the actual trace. It is intendedthat the respective detiection and variable-density traces be suchduplicates that the deiiection trace would result from scanning thevariable-density trace with a light beam and photocell, for example, andapplying the amplied photocel] output to a galvanometer.

FIGURE 3 suggests the appearance of a portion of a well log recorded inaccordance with our invention. Thus, the log 68 corresponds to thevariable-density recording obtained from a well having the lithologyindicated by the lithologic log 69 on the left, using an instrument 11and recording system such as is shown in FIGURE l. The edge 70 forms abase line parallel to the edge ot film strip 46 corresponding to zerotime, when pulse emission by transmitter l2 occurs, while edge 71corresponds to a time about two milliseconds later. The distance frombase line 70 varies linearly with time in this twomillisecond interval.The width of the uniform-density area between base line 70 and the firstwave arrivals is thus directly' proportional to the pulse travel timethrough the formation, and is therefore inversely proportional to theformation seismic compressional-wave velocity. Thus, the log 68 containsall the information present on a tirstarrival log and in addition showsthe amplitude, phase, frequency, and arrival times of the subsequentwaves. Obviously, much more information is available here for lithologicinterpretation.

Furthermore, the changes in wave form as the logging instrument passesfrom one formation to another are indicated much more clearly on thecommon time scale than they would be on separate deflection traces eachwith its own scale.

The choice of. the speed of movement, or the depth scale factor, ofthefilm 46 in relation to the logging speed, to the pulse-repetition rateof transmitter 12, and to the thickness of the trace 38 or its image 52is a matter of some importance. It is preferred that they be so relatedthat the photographic exposure at any point of film 46 is the resultantof several sweeps of the oscilloscope beam. Any random noisesuperimposed on the desired signal in one sweep then tends to cancelrandom noise on another sweep while the desired signals all combineadditively. Thus, the final recording of the wave form at any point ofdepth is the summation of a number of similar wave forms. It has ahigher signal-to-noise ratio than is likely for any single member of thesummation. Accordingly, when this method of recording is used, therequired amplitude of pulse emission by transmitter 12 is reduced forresults with the signal-to-noise ratio now considered acceptable. Oralternatively, pulses of the strength now employed can be transmittedover larger distances than have been considered feasible heretofore.

Although the application of the invention to seismic velocity loggingwith a single detector has been described in detail, it can also be usedwith two-detector logging instruments, wherein the difference in arrivaltimes at the two differently spaced detectors is the most importantquantity for showing velocity. Preferably each of the two receiversintensity-modulates the beam of one of a pair ot cathode-rayOscilloscopes, just as the single receiver 13 does oscilloscope 31 inFIGURE 1. The images of the two oscilloscope traces are preferablyplaced side by side on the film 46, so that the log produced appears astwo parallel bands each similar to log 68. Besides showing in this waythe complete wave trains arriving at each of the two receivers, thedesired difference in first-arrival times, on the time differencebetween any other wave arrivals, such as the shear-wave arrivals at thetwo detectors, can be determined simply by scaling the distance betweenthe arrivals in the two bands. This assumes that the sweep velocities ofthe two Oscilloscopes are the same, which can be assured by using thesame sweep generator for both,

While our invention has been described by reference to the foregoingdetails and examples, its scope should not be considered as limited tothese details, but is properly to be ascertained from the appendedclaims.

We claim:

1. The method of recording seismic well logs while moving a seismicimpulse transmitter and a receiver of seismic waves through a well atsubstantially constant speed while maintaining sai-d transmitter andreceiver a small fixed distance apart and repeatedly causing saidtransmitter to emit impulses and said receiver to detect the resultantseismic waves impinging thereon, which recording method comprises movinga record-receiving strip lengthwise in proportion to the speed of movingsaid transmitter and receiver through said well, initiating a mark at abase line parallel to the edge of said strip substantially synchronouslywith the emission of each impulse by said transmitter, extending saidmark continuously and linearly with time across said strip in thedirection of its width during the time interval while the seismic wavesresulting from said impulse are traveling to and are being received bysaid receiver, and varying the density of said mark in proportion to theinstantaneous amplitude of the waves received by said receiver.

2. A method as in claim 1 in which said recording method comprisesmoving a photosensitive record strip lengthwise at a rate proportionalto the speed of moving said transmitter and receiver through said well,projecting an exposure-producing light beam of intermediate intensityonto said strip at a constant distance from its edge in synchronism witheach emission of an impulse by said transmitter, sweeping said beamtransversely across said strip in the direction of its width at asubstantially constant rate during the time of traveling and arrival atsaid receiver of the resultant waves of said each impulse emission, andvarying the intensity of said beam from said intermediate intensity inproportion to the instantaneous positive and negative amplitudes of thewaves impinging on said receiver.

3. A recording method as in claim 2 in which the distance of lengthwisemovement of said strip in the time interval between any two successivepulse emissions by said transmitter is substantially less than thethickness of said beam, whereby the exposure at any exposed point onsaid strip accumulates during a plurality of sweeps of said beam.

4. The method of recording seismic well logs while moving a seismicimpulse transmitter and a receiver of seismic waves through a well at aspeed which may vary while maintaining said transmitter and receiver asmall fixed distance apart and repeatedly causing said transmitter toemit impulses and said receiver to detect the resultant seismic wavesimpinging thereon, which recording method comprises moving arecord-receiving strip lengthwise in proportion to the speed of movingsaid transmitter and receiver through said well, initiating a mark at abase line parallel to the edge of said strip substantilaly synchronouslywith the emission of each impulse by said transmitter, extending saidmark linearly with time across said strip in the direction of its widthduring the time interval while the seismic waves resulting from saidimpulse are traveling to and being received by said receiver, varyingthe instantaneous density of said mark in proportion to theinstantaneous amplitude of the waves received by said receiver, andvarying the average density of said mark in proportion to the speed ofmoving said transmitter and receiver through said well.

5. A method as in claim 4 in which said recording method comprisesmoving a photosensitive record strip lengthwise at a rate proportionalto the speed of moving said transmitter and receiver through said well,projecting an exposure-producing light beam of intermediate intensityonto said strip at a constant distance from its edge in synchronism witheach transmission of an impulse by said transmitter, sweeping said beamtransversely across said strip in the direction of its width at asubstantially constant rate during the time of traveling and arrival atsaid receiver of the resultant waves of said each impulse emission.varying the instantaneous intensity of said beam from said intermediateintensity in proportion to the instantaneous positive and negativeamplitudes ofthe Waves impinging on said receiver, and varying saidintermediate intensity in proportion to the speed of moving said seismicimpulse transmitter and receiver through said well.

6. A recording method as in claim 5 in which the distance of lengthwisestrip movement in the time interval between successive pulse emissionsby said transmitter is substantially less than the thickness of saidbeam in the lengthwise direction of said strip, whereby the exposure atany exposed point on said strip accumulates during a plurality of sweepsof said beam.

7. Apparatus for recording seismic well logs while moving a seismicimpulse transmitter and receiver of seismic waves through a well atsubstantially constant speed While maintaining said transmitter andreceiver a small fixed distance apart and repeatedly causing saidtransmitter to emit impulses and said receiver to detect the resultantseismic waves impinging thereon, said recording apparatus comprisingmeans for moving a recordreceiving strip lengthwise at a rateproportional to the rate of movement of said transmitter and receiver insaid well, means actuated by said transmitter for producing transversemarks of an intermediate density on said strip, each of said marksstarting from a base line parallel to the strip edge in synchronism withthe emission of an impulse by said transmitter and being drawn acrosssaid strip during the travel and arrival of the resultant seismic wavesat said receiver, and means actuated by said receiver for controllingsaid mark-producing means to vary said intermediate density of markingin proportion to the instantaneous values of the amplitude of the wavesreceived by said receiver.

8. Apparatus as in claim 7 wherein said recording apparatus comprisesmeans for moving a photosensitive record strip lengthwise at a rateproportional to a speed of movement of said transmitter and receiverthrough said well, a source of exposure-producing light, means actuatedby said transmitter for projecting an exposureproducing beam ofintermediate intensity from said light source onto said strip at aconstant distance from its edge in synchronism with each emission of animpulse by said transmitter, means for sweeping said beam transverselyacross said strip in the direction of its width at a substantiall),rconstant rate during the time of traveling and arrival at said receiverof the resultant waves of each impulse emission, and means actuated bysaid receiver for varying the instantaneous intensity of said beam fromsaid intermediate intensity in proportion to the instantaneous positiveand negative amplitudes of the waves impinging on said receiver.

9. Apparatus as in claim 8 in which the thickness of said beam in thelengthwise direction of said strip is substantially greater than thedistance of lengthwise strip movement between successive pulse emissionsby said transmitter, whereby the exposure at any exposed point on saidstrip accumulates during a plurality of sweeps of said beam.

10. Apparatus for recording seismic well logs while moving a seismicimpulse transmitter and a receiver of seismic waves through a well at aspeed which may vary while maintaining said transmitter and receiver asmall fixed distance apart and repeatedly causing said transmitter toemit impulses and said receiver to detect the resultant seismic waveimpinging thereon, said recording apparatus comprising7 means for movinga record- !eceiving strip lengthwise in proportion to the movement ofsaid transmitter and receiver in said well, means actuated by saidtransmitter for initiating marking of said strip at a base line on saidstrip parallel to one edge thereof in synehronism with the emission ofan impulse by said transmitter, means for extending the mark produced bysaid mark-initiating means across said strip at a constant rate duringthe time of travel and arrival of the seismic waves resulting from saidimpulse at said receiver, means actuated by said receiver for varyingthe density of marking of said strip above and below an average densityin proportion to the positive and negative instantaneous amplitudes ofthe wave impinging on said receiver, means responsive to the speed ofmovement of said transmitter and receiver, and means actuated by saidspeedresponsive means to change said average density in proportion tochanges in said speed.

11. Apparatus as in claim It) wherein said recording apparatus comprisesmeans for moving a photosensitive record strip lengthwise in accordanceWith the movement of said transmitter and receiver through said well, alight source, means for projecting a beam of exposure-producing lightfrom said source onto said record strip, means for sweeping said beamacross said strip in the direction of its width at a substantiallyconstant rate, means actuated by said transmitter for initiating thesweeping of said beam by said beam-sweeping means at a base line on saidstrip synchronously with the emission of each impulse by saidtransmitter, means actuated by said receiver for varying the intensityof said beam impinging on said strip from an average value in proportionto the positive and negative instantaneous amplitudes of the wavesimpinging on said receiver, means responsive to the speed of movement ofsaid transmitter and receiver through said well, and means actuated bysaid speed-responsive means tor varying the average value of saidintensity in proportion to the variations of said speed detected by saidspeed-responsive means.

12. Apparatus as in claim 11 in which the thickness of said beam in thelengthwise direction of said strip is substantially greater than thedistance of lengthwise strip movement between successive pulse emissionsby said transmitter, whereby the exposure at any exposed point on saidstrip accumulates during n plurality of sweeps of said beam.

J3. The method of recording scismic wcll logs while moving a .reis/nicimpulse transmitter and o receiver of seismic waves through o wcll utsubstantial] y constant .vpccd while maintaining .void transmitter ondrcccivcr o smo/l hxed distance npr/rt onfl repeatedly causing saidtrousmitter to emit impulses and said rcccivcr to dctcct thc rc-.sultont seismic waves impinging thereon, which recording methodcomprises moving a record-receiving strip lcngtltwis@ in proportion tothc .speed of moving,7 said transmitter und rcccivcr through said well,initiating o mark ot a hust line porollcl to the cdgc of said strip.sulmtontiolly in syncllronisnz with thc transmission of cach impulsethrough the wcll formations', attending said mark continuous/y andlinearly with time across sold strip in the dircction of its widthduring the time interval whi/c thc seismic waves rcsulting from saidimpulse are being rcccivcd by said rcccivcr| and varying thc dtuzsity of.void mor/c in proportion to thc instuntuncrms amplitude of the wnvcsreccivcd by sold rcccivcr.

14. A method os in cluim I3 in which scid recording method comprisesmoving o photoscnsitive record strip lengthwise at n rote proptnlionnlto thc spccd of moving soid transmitter und rccciver through said wcll,projecting un exporme-producing light beam of intermediate intensityonto suid strip ot u constant distance j rom its edge in synchronismwith the transmission of cach impulse through tht7 well formations,swccping sold hcom tronstfcrscly across .mid strip in the direction ofits width ot a substanrial/y constant rate during the time of arrivo] otsaid rcccivcr of the resultant waves of cach impulse emission, andtutrying thc intensity of .raid bcnm from said intermediate intcnsity inproportion to the instantaneous positive und negative mnplitudcs of theuf'ovcs impinging on said receiver.

I 5. Apparatus for recording seismic wcll logs by moving a seismicimpulse transmitter and o rcccivcr of seismic waves through o well at.substantially constant spccd while maintaining said transmitter undreceiver n sn'zall )fixed distance apart and repeatedly causing saidtransmitter t0 @mit impulses und .mid receiver to detcct the resultant.seismic waves impinging thereon, said recording apparatus comprisingmeans for moving u record-rccciving strip lengthwise at a roteproportional t0 thc rntc of movement of soid transmitter and rcccivcr insaid well, means uctuotcd in synchro/:ism with the transmission of euchimpulse through the well formations for producing transverse marks of anintermediate density on said strip, each of said marks starting from ubose linc patrol/cl to the strip ridge ond being drawn across .saidstrip during the arrival of the resultant seismic waves at saidreceiver, und means actuated by said receiver for controlling saidmark-producing means to vary .mid intcrmcdiotc density of murking inproportion to the instantaneous volucs of the amplitude of the wavesreceived by said receiver.

I6. Apparatus os in claim l5 whcrcin said recording oppnratuscon'ipriscs moans for moving a photoscnsitivc record strip lengthwise oto rouI proportional to the speed 0f movement of .mid transmittcr undreceiver through said tvc/l, n source of cxposurta-producing light,mcons actuated in synchro/risul with thc trnnsmission of cach impulsethrough thc wel! formations for projecting on avposnrcproducing hmm ofintermediate intcnsity from .mid light source onto said strip ot oconstant distance from its cdgc, mcons for sweeping Suid hcamtransverse/ v across said strip in the direction of its width at r1substantially constant rote during the time of arrival at soid rcccivcrof thc resultant wovcs of cach impulse emission, and mcons nctuotcd bysaid rcccivcr for varying thc instrmtoncous intensity of said bcnm from.said intcrmcdint@ intensity in proportion to the instantaneous positiveund negative amplitudes of the waves impinging on snid rcccivcr.

References Cited by the Examiner The following references, cited by `theExaminer, are of record in the patented tile of this patent or theoriginal patent.

(Other references ou foilowing page) UNITED 9 STATES PATENTS Lehmann179-1003 McCormick 346-110 Vrick 315-24 Summers 181-.5 Eisler 346-74 102,907,621 10/1959 Eisler 346-74 3,048,847 8/ 1962 Frost et a1. 346-1103,081,838 3/1963 Platt 181-.5

5 BENJAMIN A. BORCHELT, Primary Examiner.

W. KUJAWA, Assistant Examiner.

